The present invention relates to an integrated battery, more specifically, to a flexible battery in which a plurality of unit cells are arranged on a flexible substrate.
As devices including cell phones are made smaller and their performance is improved in recent years, demand is increasing for the development of batteries as power sources for such devices. For example, the research and development of a lithium ion battery with a higher energy density and the commercialization thereof are rapidly proceeding. In such battery, an electrolyte solution comprising a liquid such as organic solvent has been used as a medium for transferring ions, which is accompanied by a possibility of leakage of an electrolyte solution from a battery.
In order to solve the problem that could harm the reliability of a battery containing such electrolyte solution, studies of an all-solid battery are under way. There are proposed, for example, an all-solid battery using a solid polymer electrolyte, instead of an electrolyte solution (see, for example, Japanese Patent Laid-Open No. 2000-251939), and an all-solid battery using an inorganic solid electrolyte (see, for example, Japanese Patent Laid-Open Nos. Sho 60-257073 and Hei 10-247516).
With the miniaturization of such devices, studies of a thinner all-solid battery are also being carried out. In order to achieve a thin all-solid battery, a proposal is made that a positive electrode, a solid electrolyte, a negative electrode and the like are formed on a certain substrate by a thin film forming process in a vacuum such as sputtering method, ion plating method and deposition method (see, for example, U.S. Pat. Nos. 5,338,625 and 5,141,614).
In order to increase capacity and to achieve a high voltage, for example, Japanese Patent Laid-Open No. Sho 61-165965 discloses that a plurality of solid cells connected in series or parallel are formed on one substrate by patterning using a mask. Further, Japanese Patent Laid-Open No. Hei 8-064213 discloses that a plurality of thin cells are stacked, wherein each thin cell comprises a positive electrode active material, a solid electrolyte and a negative electrode active material. The positive electrode active material, the solid electrolyte and the negative electrode active material are interposed between facing positive and negative electrode current collectors that also may function as jackets. In the thin cell, the peripheral area of the positive electrode current collector and that of the negative electrode current collector are adhered each other by a resin frame, and the resin frame is protruded to the outside of the peripheral area. A plurality of such thin cells are stacked and the protruded portions of the resin frames are adhered to form one stacked cell.
Solid cells as described above are typically formed on a substrate. The substrate is usually made of quartz, alumina, silicon wafer, sapphire, etc. The substrates made of such materials have excellent thermal resistance, but are usually thick and rigid. In other words, they are inflexible. Because of this, if a thin device such as IC card or RFID tag comprising such solid cell is excessively bent or twisted, the cells might be broken or cracked, resulting in decreased battery characteristics or breakdown of a battery.
In order to improve the tolerance against bending, one option is to make cells with a smaller dimension, but the battery capacity will be small.
Another option is to produce a substrate using a flexible material. A substrate made of flexible material can be made thinner than conventional substrates made of quartz, alumina, silicon wafer, sapphire, etc. Accordingly, it is possible to achieve a higher volume energy density compared to the case of using the conventional substrates.
However, if one large solid cell is formed on a flexible substrate to give a battery and the battery is bent, there is a possibility that only the solid cell is damaged, due to less flexibility of the solid cell.
Given the above, in order to achieve the tolerance against repeated bending as well as repeated impact and to attain high reliability of a battery, Japanese Patent Laid-Open Nos. 2000-195482 and 2001-15153 disclose a plurality of solid cells being arranged on a substrate in a lattice pattern, each of the solid cells having a rectangular shape and comprising a power-generating element in which a positive electrode active material, a solid electrolyte and a negative electrode active material are stacked to form a layered structure.
The battery as described above reduces a possibility of destruction of the solid cells in the case where the battery is bent along a line parallel to a side of the solid cell. The battery, however, still has a great possibility of destruction of the solid cells in the case where the battery is twisted or bent along a line parallel to a diagonal line of the solid cell.
In view of the above, it is an object of the present invention to provide a battery having sufficient capacity that can function without being damaged even if the battery is twisted.